Beam clearing and resetting circuit



M 1959 R. w. WOLFE ET AL 2,877,373

' BEAM CLEARING ANDIRESETTING cmcun' Filed Feb. 21; 1958 PULSE SOURCE MULTI- VI RA'roR INVENTOR ROGER W WOLFE By WILLIAM I de l/[Nfikkf ATTO RNEY I beam thus formed may be moved operating voltages. .ing the spade electrode at the selected 2,877,378 BEAM CLEARING AND RESETTING CIRCUIT a a w. Wolfe, South Plainfield, and William I. deVel-sterre, Bound Brook, N. J., assignors to Burroughs Corporation, Detroit, Mich., a corporation of Michlgan i Application February 21, 1958, Serial No. 716,759-

' i 1 Claims. (Cl. 315-21) This invention relates generally tomulti-position electron beam switching tubes and to systems for clearing an electron beam from a position in the tube and resetting the beam in a selected Of position.

One type of multi-position electron beam switching tube, to which the principles of the invention apply, is described in U. S. Patent No. 2,721,955 of Fan et al. This type of tube includes a central cathode which is surrounded by a plurality of groups of electrodes, each group representing a position at which an electron beam may form and including a target electrode for receiving an electron beam and developing an output signal therefrom, and a spade electrode adapted to form and hold an electron-beam on its associated target electrode. Each group of electrodes may also include a switching electrode for switching an electron beam from one group of electrodes .to the next under the influence of crossed electric and magnetic fields.

Generally, in the operation of a tube of this type, with all of th e tube electrodes carrying their normal supply voltages, electrons emitted by the cathode are retained in the vicinity of the cathode, and an electron beam does not form in any of the tube positions. When a spade or switching electrode has its electrical potential suitably reduced, the electric field pattern is altered and an electron beam forms on a target electrode associated with that spade or switching electrode. Ordinarily, the electron I from one position: to the next by means of suitable electrical pulses applied to the switching electrodes.

In some applications of these tubes, for example in decade counters or the like, it is desirable to be able to allow the tube to execute a predetermined counting operation, that 'is, to move from position to position until it reaches a predetermined position and then to clear the tube and reset the electron beam at a selected 0 position. Circuits are known for clearing and resetting tubes of the type described above. Inone circuit of this type,

are reduced from their normal common low reference potena position in the tube, and then return to their normal positive Circuit means are provided for causposition to rise more slowly than the other spades so that the 0 spade has a lower potential than the other spades for a period of time and, as a result, an electron beam forms at the 0" position. However, inter-electrode capacities at the 0 position adversely affect this desired sequence of operations, for example, by undesirably limiting the speed at which they may be executed and by preventing the 0 spade from reaching a sufliciently low potential.

Accordingly, provide an improved circuit for clearing and resetting an electron beam in a multi-position electron tube.

Another object of the invention is to provide animproved high speed circuit for clearing and resetting an all of the spade electrodes positive bias potential to a tial to clear a beam from the spades are allowed to electron beamin a rnulti-positiomelectron. tube. a

one object of the present invention is to by a suitable time delay network coupled to the 0" spade.

,target electrode.

. netie fields withinthe tube.

2,877,378 Patented Mar. 10, 19 59 through spade load resistors to a spade buss through which supply voltage is provided for the spade electrodes. Means are provided coupled directly to the spade buss, for

- reducing the potentials of all of the spade electrodes from their normal positive operating potentials to a lower level at which an electron beam cannot be held thereby on any target electrode. This means maybe a source ofnegative pulses, called clearing pulses, and this operation clears the tube of an electron beam which might have been .flowing to oneof the target electrodes.

' According to the invention, in order to overcome interelectrode capacities at the 0 position and to insure that the 0 spade, aswell as the other spades, reach a sufiiciently low potential so that the tube is cleared, a low resistance diode is connected directly between the means for lowering the potentialof the spades and the 0 spade itself. Subsequently, the potentials of the spade buss and the spade electrodes are allowed to rise rapidly toward their normal operating levels. However,'the potential of the spade electrode at the selected 0 position, atwhich it is desired to reset or refo I the electron beam, rises slowly so that this 0 spade has a lower potential. than the other spades and the electron beam forms thereon. The slow rise in potential of the O spade is achieved The invention is described in ence to the drawing wherein: v

Fig. 1 is a perspective view of an electron beam switching tube of a type useful in practicing the invention; and

Fig. 2 is a schematic representation of the tube of Fig. l and a circuit in which it may be operated according to the invention. H g

The invention is described herein as it applies to a multiposition electron beamvtube of the type shown in U. S. Patent No. 2,721,955 to Fan et al. This type of tube, 10 is shown in Fig. l-and includes, briefly, an envelope 12 which contains a central longitudinally elongated cathode 14 and ten groups of electrodes spaced radially from the cathode and surrounding the cathode. Each group .of electrodes includes a generally U-shaped elongated spade electrode- 16and a target electrode 18 positioned so that eachtarget occupies the spacebetween: adjacent spade electrodes. Each spade electrode serves to form and hold an electron beam on its associated target electrode from which an output signal may be derived. A generally rodlike switching electrode 20 is also included in each group of electrodes and is positioned between one edge of each target electrode and the adjacent spade electrode. An open-ended cylindrical permanent magnet 22 is provided surrounding the tube envelope and coaxial therewith. The magnet provides an axial magnetic field which is utilized in conjunction with electric fields within the tube to forin and switch an electron beam from the cathode to each of the groups of electrodes.

Briefly, in operation of tube 10, electrons emitted by the cathode are retained at the cathode if each of "the spades, targets and switching electrodes carries its normal greater detail by refer- ;opera'ting electrical potential. When a spade or switching electrode experiences an appropriate change in potential, an electron beam is formed and directed "to a The electron beam may be switched from one, target electrode to the next by thus suitably altering the electrical potentials of a spade or switching electrode. The direction in which a beam may be switched is determined by the orientation of the electric and mag- A circuit embodying the invention is shown in Fig. 2 wherein the tube 10 is shown schematically in linear form. To simplify the drawing, only three of the usual ten positions or groups of electrodes are shown. These positions are numbered "0, 1, and 9. In the circuit shown in Fig.2, the cathode 14 is connected through a cathode resistor 24 to asource of reference potential such as ground. Each spade electrode 16 is connected through a spade load resistor 26 to a common spade buss 28. The spade buss 28, in turn, is connected through a common spade load resistor 30 to a positive D. C. supply voltage, V of about l50 volts and a source 32 f negative pulses 34. Each target electrode 18 is coupled through a load resistor 38 to a common target buss 40 which, in turn, is connected to a positive D. C. supply voltage, V of about 300 volts. An output terminal 41 isprovidedat each target and is adapted to be connected to a suitable utilization device or circuit.

The switching electrodes 20 which are employed to switch an electron beam from-position to position Within the tube may be connected in any one of a number of suitable ways to provide the desired switching operation. According to one suitable arrangement as shown, the switching electrodes are connected in two sets, with alternate electrodes being connected together to form a set. The two sets of switching electrodes are coupled to a suitable source of switching pulses such as a bistable multivibrator 42. The output pulses from each side of the multivibrator serve to switch the electron beam from one position to the next.

In the circuit of Fig. 2, means are provided for clearing and resetting an electron beam within the tube 10. For purposes of illustration, the circuit shown is adapted to clear the tube and reset the beam at the 0" position. The circuit includes the aforementioned source 32 of negative pulses 34 coupled directly to the spade buss 28. The time duration of the pulses 34 is determined by the length of time required to clear an electron beam from one of the positions in the tube with the spades at the selected reduced voltage which may be about 100 volts. At the 0 position, an auxiliary impedance, for example a resistor 46, is provided between the spade resistor 26 and the spade buss 28. According to the invention, means are provided at the "0 position for assisting the 0 spade in reaching the low potential level produced by the pulses 34 and required for clearing an electron beam from the tube 10. This means also insures that the 0 spade reach at leastthe same or a lower potential than the other spades when the beam clearing operation is performed. This means comprises a unidirectional current flow device, for example, a diode 47, having its anode connected to the 0 spade and its cathode connected to the spade buss, or, in effect, to the pulse source 32. The diode 47 is thus oriented to pass the negative pulses 34 readily to the "0 spade.

In addition, a time delay circuit is coupled to the 0 spade to control the rate at which the "0 spade rises from the low potential produced by the pulses 34 to its higher positive supply potential. In the time delay ciromit, the spade buss 28 is connected through a diode 48 and a capacitor 50 to ground. The diode 48 isoriented to provide easy current flow to the spade buss and spade voltage supply source, V from the capacitor 50. The junction point of the diode 48 and capacitor 50 is connected to the junction point of the resistor 46 and the 0 spade resistor 26. The resistor 46 and capacitor 50 are selected to provide the desired circuit time constant.

In operation of the circuit of .Fig. 2, let it be assumed that the tube 10 is counting in normal fashion and an electron beam is being switched from position to position under the influence of pulses applied to the switching electrodes from the multivibrator 42. When it is desired to clear and reset the tube, a negative pulse 34 is applied to the spade buss 28. The pulse 34 hasan'ainand hold an electron plitude of about volts and lowers the spade buss and the spade electrodes from 150 volts to about 50 volts. The diode serves to insure that the 0 spade is lowered to at least 100 volts just as the other spades are lowered. Since all of the spade electrodes are at the same potential, the electron beam is cleared from the position in which it was formed and electrons are held in the vicinity of the cathode under the influence of the crossed electric and magnetic fields in the tube. The pulse 34 passes quickly through the low resistance diode 48 and reduces the potential of the capacitor 50 from about volts (to which it had been charged) to about 40 volts. When the pulse 34 from the pulse source 32 is terminated, the spade buss 28 returns to its normal operating voltage level of about volts as determined by the supply voltage, V and all of the spade electrodes return to their normal operating voltages of about 150 volts except the spadein the 0 position. This spade is maintained initially at a reduced voltage of about 50 volts by the charge on the capacitor 50, and the rate at which this spade returns to normal operating voltage is determined by the time constant of the resistor 46 and capacitor 50. Since the spade at the 0 position is thus maintained at a lower potential than the other spades for a period of time, an electron beam from the cathode 14 forms on the target 18 at the 0 position under the influence of the spade at this position.

In a typical circuit, the target resistors have a value of about 18,000 ohms; the spade resistors have a value of about 100,000 ohms; the resistor 46 has a value of about 20,00 ohms; and the capacitor has a value of about 100 pf. The pulses 34 have a magnitude of about -l00 volts and a time duration of about one microsecond. In such a circuit, it is possible to clear and reset an electron beam in about one microsecond.

What is claimed is:

1. An electron beam clearing and resetting circuit for a multi-position electron beam tube comprising an electron beam tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode; each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; a common spade buss; a spade impedance coupled between each of said spade electrodes and said common spade buss; first circuit means connected to said spade buss for changingthe potential of the buss and the spade electrodes at a predetermined rate between a positive reference potential and a lower potential; second circuit means coupled to a selected spade electrode for assisting it in reaching said lower potential; and third circuit means coupledto said seelcted spade electrode for raising the potential thereof from said lower potential to said reference potential at a slower rate than the other of said spade electrodes so that, for a time, the potential of said selected spade is lower than the potentials of the other spades and an electron beam forms on the target electrode associated with said selected spade electrode.

2. A circuit defined in claim 1 wherein said second circuit means includes a diode connected between said buss and said selected spade and said third circuit means includes a resistoncapacitor network and a diode, said first-mentioned diode being connected across the spade resistor of said selected spade.

3. A beam clearing and resetting circuit for an electron beam switching device comprising an electron beam switching tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode; each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form beam on its associated target electrode; a spade impedance coupled between each of said spade electrodes'anda common spade buss; an auxiliary impedance between said spade buss and the load impedance connected to a selected one of said spade electrodes; first circuit means connected to said spade buss for changing the potential thereof at a certain rate between a positive operating potential and a lower reference potential; second circuit means coupled between said first circuit means and said selected spade electrode for assisting it in reaching said lower reference potential; and third circuit means coupled to said selected spade electrode for raising the potential thereof from said reference potential to said operating potential at a slower rate than the other of said spade electrodes so that momentarily said selected spade is at a lower potential than the other spades and an electron beam forms on the target electrode associated with said selected spade electrode.

4. The circuit defined in claim 3 wherein said second circuit means includes a diode and said third circuit means includes a capacitor coupled between a source of reference potential less positive than said operating and reference potentials and the junction point of the auxiliary impedance and the spade impedance of said selected spade electrode, and a low resistance diode connected across said last-named spade impedance.

5. The circuit defined in claim 3 wherein said third circuit means includes a crystal diode connected between the junction point of the auxiliary impedance and the spade impedance of said selected spade electrode and a source of reference potential lower than said operating potential and said lower reference potential.

6. A beam clearing and resetting circuit for an electronic switching device comprising an electron beam switching tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode; each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; a spade buss; means for applying a positive operating potential to said spade buss and to said spades; a spade impedance coupled between each of said spade electrodes and said common spade buss; an auxiliary impedance between said common :buss and the load impedance connected to a selected one of said spade electrodes; a source of negative voltage pulses coupled to said spade buss for applying negative pulses to said spade buss and thereby lowering the potential of said buss and said spade electrodes from said operating potential to a lower reference potential; auxiliary means coupled between said spade buss and selected spade electrode for assisting in lowering its potential; and means coupled to said selected spade electrode for raising its potential from the lower reference potential to said operating potential at a slower rate than the other of said spade electrodes when a negative pulse is not present at said spade buss so that said selected spade electrode is, momentarily at least, at a lower potential than the other of said spade electrodes and an electron beam forms on the target electrode associated with said selected spade electrode.

7. A beam clearing and resetting circuit for an electron beam switching device comprising an electron beam switching tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode; each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; a common spade buss to which each of said spades is connected; separate sources of high and low reference potentials coupled to said spade buss; means coupled between said spade buss and a selected one of said spade electrodes for assisting in lowering its potential from said high reference potential to said low reference potential; and time delay means coupled to said selected one of said spades for raising said selected spade from said low reference potential to said high reference potential at a slower rate than the other of said spade electrodes are raised so that said selected spade has, at least momentarily, a lower potential than the other spades and an electron beam forms on the target electrode associated with said selected spade electrode.

No references cited. 

